Polyethylene glycols from etherestes of glycolic acid



Patented Oct. 6, 1953 POLYETHYLENE GLY ESTERS OF G COLS FROM ETHER-LYCOLIC ACID William F. Gresham, Wilmington, Del., assignor to E. I. duPont de Nemours and Company, Wilmington, Del., a corporation of DelawareNo Drawing. Application December 8, 1949, Serial No. 131,939

5 Claims. (Cl. 260615) This invention relates to a process for thepreparation of glycols by the hydrogenation of ether-esters ofhydroxyacetic acid and is more particularly related to the preparationof diethylene glycol and triethylene glycol by a twostep process, in thefirst step of which hydroxyacetic acid is esterified and etherified to acomplex ether-ester and in the second step or which the ether-ester ofthe first step is hydrogenated.

The course of the reaction is illustrated by these simplified equations:(1) 2 HOCH2CH2OH+HOCH2COOH+ HO CHECHSO cngcoocn ongon (A) 2Il- -O (2 3I-lOCH CH2OH+'2 nocn coon-s 3) 2 HOCH 'COOH+HOCH2CHzOCH2CHgOH+HOCHzCHzOH- (HOCHZCHQOCOCHQOCHZ CH;OCH2CH::0COCH2OH(B) 31520 Theyrepresent the esterification and etherification of hydroxyacetic acidwith ethylene glycol or diethylene glycol. The actual reaction givescomplex glycol ether-esters of hydroxyacetic acid. The complexether-ester (A) of Equation 1 on hydrogenation is converted to ethyleneglycol iv and diethylene glycol While the complex etherester (B) ofEquation 3, on hydrogenation, is converted principally to triethyleneglycol and ethylene glycol. Other more complex etheresters are formedduring the esterification and etherification reaction and as aconsequence other glycols are produced during the hydrogenation of thecomplex mixture of ether-esters.

The equations show, inter alia, the overall preparation of ethyleneglycol, diethylene glycol and triethylene glycol from hydroxyacetic acidand ethylene glycol. Ethylene glycol and diethylene glycol, products ofthe hydrogenation, will recombine with hydroxyacetic acid, thesereactants may be returned in a cyclic process with the result that thebasic materials for the reaction constitute essentially hydroxyaceticacid and hydrogen.

An object of the present invention is to provide a process for thepreparation of diethylene glycol and triethylene glycol. Another objectof the invention is to provide a process forthe etherification of aglycol ester of hydroxyacetic acid. Yet another object is to provide aprocess for the simultaneous production of diethylene glycol andtriethylene glycol from the hydrogenation of a complex ether-esterproduced by the etherification of a glycol ester of hydroxyacetic acid.Yet another object is to provide a continuous process for thepreparation of diethylene glycol and triethylene glycol. Other objectsand advantages of the invention will hereinafter appear.

In accord with the preferred embodiment of the invention, theesterification and etherification of hydroxyacetic acid are conducted instep one to produce complex ether-esters which, in step two, arehydrogenated to give ethylene glycol, diethylene glycol, triethyleneglycol and higher glycols. The reactions in step one are necessarilycomplex because of the many possible reactions that may occur betweenhydroxyacetic acid, and the glycols introduced. In the hydrogenationstep, the complex ether-ester is hydrogenated to a mixture of ethyleneand polyethylene glycols. The ethylene glycol and diethylene glycol canbe returned to the reaction and only the desired polyethylene glycolseparated, by this means it is possible to conduct the reaction for theproduction of a single polyethylene glycol.

One manner of conducting the consolidated estcrification andetherification step of the process is by mixing hydroxyacetic acid withethylene lycol and/or recycled diethylene or other polyethylene glycols.This esterification-etherification reaction is conducted in the presenceof a mild catalyst under conditions such that the production of dioxaneand other undesired byproducts are restricted. 'I'he hydrogenation stepis carried out in accord with one modification of the reaction bycontinuously hydrogenating a mixture of the complex ether-esterintermediate of the first step to the polyethylene glycols. The productsof the hydrogenation step are distilled at reduced pressure, wherebytriethylene glycol is separated from the ethylene glycol and other glycols which may be recycled. The process may be conducted continuously orby batch methods although the former is more economical for commercialproduction.

The more detailed practice of the invention is illustrated by thefollowing examples in which parts are by weight unless otherwise stated.

Example 1.-A mixture of ethylene glycol and hydroxyacetic acid wasplaced in a suitable converter provided with a reflux condenser, thereglycol to hydroxyacetic acid may range between 1.25:1 to 7:1, SuperFiltrol X3580 (an acid activated bentonite clay manufactured by theFiltrol Company) is employed as the catalyst and the temperature raisedto about 185 C. and held for desired by droxyacetic acid and cation retalyst. The

action is then conducted at a is manner.

Prior to ihed has been erification and roxyacetic acid, the proateri:ietween 120 and presence, or

talysts, may be These reactions nder pressures rangatmospheres.

tion catalyst such hromium, metal chromite res thereof.

d clays generally. milar ca employed in concentrations 0 ded thatsubstanter of etherification and esteriss herein descr imultaneoiis estr 40 see may likewise be conducted if d in this manner, may be t re 1about 2 hours in the 95 C. for 1 to 6 hours.

ltaneous esterificatiou a weakly acidic cata- Super Filtrol XBBSC,

f 2 to about 10% of With these, and similar cataremove the water ofesteri- 1 reaction and to accom dioxide or other inert gas such may bepassed through the reaction. The reaction with these catalysts, and withthe oxide or other inert gas 2 to hours at a tem- 150 and 195 C. Verylittle, if any, degradation of the hydroxyacetic acid, or

eration in th tion may be conducted 150 and 300 C. with there isconsiderable While the proce conducted with a s etherification o1"; h

first esterifying the hy thereafter etheri'fying it. The e action, whenconducte carried out at a tempera 160 C. for

absence, of a mild esteriiication ca etherification re temperature of160-1 For conducting the simu and etherification reaction lyst ispreferred such as boron fluoride, and acidifie These catalysts, and sithe liquid charge.

lysts, it is advisable to cation during the dua plish this carbon asnitrogen introduction of carbon di is accomplished in from peraturebetween the glycols, results from op The hydrogenation reac at atemperature between any suitable type of hydrogena F as a nickel,copper, c catalysts or mixtu are preferably conducted u ing between andhydrogenation it is recommen W tially all of the wa fieation be removedfor if ng a carbon in order water of esterification. ification catalys e213 l glycolate Equilib- M for 30 storm glycol. esters or ture of 250 C.for 1 f a manganese chromite The hydrogenated product is then distilledand there is o d triethylene glycol ethylene glycol and di-= lene git"sed of 95.0 g. o of dieth' lene glycol etate acid (molar ratios rom toduri hile 2 cu. it./hr. of

t, 18.4 g. (10% of th 3580 is added ture raised to for two hours Waction, the flow oi card. During this period dded continuously in totalof 15.2 g. of water sponds to 90% of the g. of diethylene 0.5 g. ofglyco rbon dioxide. The catam the reaction mixture and 200 M Theequilibof 39 by the ethoxide after hydrogenated at 700 atn the presenceof 20 g. hromite catalyst. Upon distilted product, there is oblycol S.F.=an acidified clay.

Zeo Karb-H=an acidified clay. sodium methoxide and then hydrogenated at700 atmospheres at a tempera hour in the presence 0 catalyst.

btaine B. P. 116-120/1 mm, ethylene glycol. Higher boiling polyethy colsare likewise present.

Example 2.-A mixture compo ethylene glycol, 53.0 g. and 38.0 g. ofhydroxy-ac 15:05:05) is heated 1" period of two hours w dioxide ispassed through the solution to facilitate removal or The ether liquidcharge) of Super Filtroi X and the tempera in order to complete the rehon dioxide being continue 7.0 g. of ethylene glycol is a an attempt toreplace the 14.0 g. oi ethylene glycol carried overhead. A is liberatedwhich corre theoretical. In addition 2.6 col, 0.5 g. of dioxane and iscarried over by the ca lyst is filtered fro g. of dry methanol added tothe filtrate. ration is then carried out at ZOO-220 minutes in order totran polyglycolide into methyl esters. rated mixture is adjusted to a paddition of 0.1-0.2 g. of sodium m which the mixture is mospheres/25D/lhr. 1 of a manganese c lation of the hydrogena tained 153 g. oftriethylene water present the complex ether-esters will bydrogenate onlywith ditficulty.

The water may be removed either by vacuum distillation afteresterification and etherification or by passing a stream of carbondioxide, nitrogen or other inert gas, with or without the aid of a gasdispersing type stirrer, into the reaction mixture concurrently withesterification and etherification to remove the water as formed. Thelatter procedure is more advantageous because the progress of thereaction is under better control and the time of the reaction reduced.

For batchwise operation the mole ratio of hydroxyacetic acid to ethyleneglycol to diethylene glycol may range between 1:7:0 to 1:0:1 to 1.25::7.When operated continuously or batchwise for the preparation oftriethylene glycol, it has been found desirable toreturn the diethyleneglycol and ethylene glycOl formed during hydrogenation to the firststep.

With carbon dioxide, or other inert gas, any suitable gas flow may beused. With a flow of about 2 cu. ft. per hour per 0.01 cu. ft. ofreactant mixture, esterification of hydroxyacetic acid, at a temperaturebetween 120 and 170 C., required about 2 hours in the absence of anadded catalyst. Using Super Filtrol as the catalyst, etherificationoccurred readily in one to six hours at temperatures between 175 and 1950., 185 C. being the optimum temperature for the reaction. Attemperatures below 165 C. the etherification reaction is quite sluggishand at 195 C. quite rapid. Variations in reaction temperature appear tohave no appreciable effect on the final product distribution.

As a prerequisite for optimum hydrogenation these conditions should beobserved:

(1) All but traces of water should be removed from the ether-estermixture.

(2) Conversion of the ether-ester mixture by the addition of methanol ata temperature of ZOO-220 for 30 minutes is recommended to transformpolyglycolides and glycol esters present at least in part to methylesters. This procedure reduces the viscosity of the mixture. Theresulting mixture may then be more easily hydrogenated at a temperaturebetween 125 and 300 C. at pressures ranging between 300 and 1000atmospheres.

The efiect of varying th ratio of total glycols to hydroxyacetic acidhas a decided result on the distribution of products. The ratio ofethylene glycol to hydroxyacetic acid may be varied from 7:1 to 1.25:1.As the ratio of glycol to acid is lowered, the quantity of tri andhigher polyethylene glycols increases while the quantity of diethyleneglycol decreases. The efiect of recycling increasing amounts ofdiethylene glycol increases the quantity of triethylene glycol andhigher polyethylene glycols finally produced. Higher ratios of glycolsto acid can be used when diethylene glycol is recycled, as compared withthe use of ethylene glycol alone.

Iclaim:

1. A process for the preparation of polyethylene glycols which comprisesesterifying and etherifying hydroxyacetic acid with a glycol at atemperature between 100 and 225 C. in the presence of a weakly acidiccatalyst and thereafter hydrogenating the resulting complex etheresterof hydroxyacetic acid to polyethylene glycols.

2. A process for the preparation of polyethylen glycols which comprisesesterifying and etherifying hydroxyacetic acid with a glycol at atemperature between 100 and 225 C. in the presence of a weakly acidicand etherification catalyst and thereafter hydrogenating the resultingcomplex ether-ester of hydroxyacetic acid to polyethylen glycols.

3. A process for the preparation of polyethylene glycols which comprisesesterifying and etherifying hydroxyacetic acid with a glycol at atemperature between 100 and 225 C. in the presence of an acid activatedclay as the esterification and etherification catalyst and thereafterhydrogenating the resulting complex etherester of hydroxyacetic acid topolyethylene glycols.

4. A process for the preparation of triethylene glycol which comprisesesterifying and etherifying hydroxyacetic acid with ethylene glycols, inthe presence of a Weakly acidic catalyst, to complex ether-esters of theacid, hydrogenating the complex ether-ester to triethylene glycol andother polyethylene glycols, separating the triethylene glycol from theother ethylene glycols and returning the latter to the esterificationand etherification reaction.

5. A process for the preparation of triethylene lycol which comprisesesterifying and etherifying hydroxyacetic acid with ethylene glycol inthe presence of an acid activated clay to complex glycol ethers andglycol esters of hydroxyacetic acid, thereafter hydrogenating saidcomplex to polyethylene glycols and recovering therefrom triethyleneglycol.

WILLIAM F. GRESHAM.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE PREPARATION OF POLYETHYLENE GLYCOLS WHICH COMPRISESESTERIFYING AND ETHERIFYING HYDROXYACETIC ACID WITH A GLYCOL AT ATEMPERATURE BETWEEN 100 AND 225* C. IN THE PRESENCE OF A WEAKLY ACIDICCATALYST AND THEREAFTER HYDROGENATING THE RESULTING COMPLEX ETHERESTEROF HYDROXYACETIC ACID TO POLYETHYLENE GLYCOLS.